1. Field of the Invention
The present invention relates to an image forming apparatus that detect an image abnormality formed on a recording sheet, a method of controlling the same and a program for implementing the method.
2. Description of the Related Art
Conventionally, there has been image forming apparatuses that have an image abnormality detecting function of detecting the presence or absence of an image abnormality formed on a sheet and automatically stopping the apparatus according to the detection result (see Japanese Laid-Open Patent Publication (Kokai) No. 2003-136818, for example).
With the image abnormality detecting function, an image printed on a sheet by a printing section of a printer apparatus is photoelectrically read by am image reader provided on a sheet conveying path, and the resulting image is expanded in an image memory. A form frame image of a part common to all the pages, which is included in the image expanded in the image memory, is compared with a form frame image as a reference which is stored in advance in a storage device. Based upon the comparison result, an image quality abnormality detecting section detects the presence or absence of an image abnormality in the image quality printed on the sheet. When an image abnormality is detected, printing is stopped.
Thus, with the conventional image abnormality detecting function, the apparatus is automatically stopped when an image abnormality such as skewing of a sheet or density trouble of an image formed is detected. Reference values for use in determining whether or not there is an image abnormality such as skewing of a sheet or density trouble are usually set to values corresponding to a high-quality image. Thus, the possibility that even an image that is not required to have a high quality is determined as being abnormal is increased. In other words, there is the possibility that even an image that can be allowed by a user is determined as being abnormal, and therefore the number of times the apparatus is stopped is increased. As a result, wasteful operations such as retry of a job are required, considerably reducing work efficiency.